163,163 research outputs found
Using weibull mixture distributions to model heterogeneous survival data
No full textIn this article we use Bayesian methods to fit a Weibull mixture model with an unknown number of components to possibly right censored survival data. This is done using the recently developed, birth-death MCMC algorithm. We also show how to estimate the survivor function and the expected hazard rate from the MCMA output
Estudo sobre métodos de estimação de F(t) para o cálculo dos parâmetros de distribuições de Weibull com a aplicação em uma análise de falhas de garrafas PET
No full textTCC(graduação) - Universidade Federal de Santa Catarina. Campus Joinville. Bacharelado Interdisciplinar em Mobilidade.A distribuição de Weibull, desenvolvida inicialmente durante as décadas de 1920 a 1950, ficou famosa com um trabalho publicado por W. Weibull (1951) sobre a tensão de escoamento de aços. Neste presente estudo, será analisado a aplicação de diferentes métodos para se estimar F(t) para o cálculo dos parâmetros de uma distribuição Weibull, aplicando-os em resultados experimentais de testes de fadiga com Garrafas PET. Os ensaios de fadiga foram realizados em amostras de garrafas PET de 1 litro, feitas com preformas de 48g, com 1 litro de água alcalina (pH 12), escolhidas aleatoriamente e colocadas em um dispositivo de testes para realizar ciclos de pressurização a 600 kPa (6 bar). Os resultados obtidos mostram valores muito próximos, porém ao serem aplicados em cálculos de probabilidade os resultados podem divergir em até 10%. Logo, nota-se a importância de validar o método de estimação antes que seja aplicado em análises de confiabilidade
Optimal Inventory Policies for Weibull Deterioration under Trade Credit in Declining Market
No full textThe aim of this study is to develop mathematical model for Weibull deterioration of items in inventory in declining market when the supplier offers his retailers a credit period to settle the accounts against the dues. The computational steps are explored for a retailer to determine the optimal purchase units which minimize the total inventory cost per time unit. The numerical examples are given to demonstrate the retailer’s optimal decision. A sensitivity analysis is carried out to study the variations in the optimal solution.Weibull deterioration, trade credit, declining market
MODELLING OF STRESS GRADIENT EFFECT ON FATIGUE LIFE USING WEIBULL BASED DISTRIBUTION FUNCTION
No full textIn the present paper, a new approach is developed in order to take into account the stress gradient effect on fatigue life of structural components. The proposed approach is based on the weakest link concept in which the shape coefficient of the Weibull distribution becomes a function of a local damage parameter. The function simulates the experimentally observed relationship between the shape of the fatigue life distribution and the stress level. Such an approach allows one to calculate the global probability distribution of the fatigue life for notched structural components in a wide range of fatigue life regime: 104-107 cycles typically. For comparison purposes, the approach is applied to calculate the number of cycles to crack initiation of structural elements under three probability levels: 5%, 63% and 95%. The calculated lifetimes are compared with the lifetimes obtained from experiments performed on notched cruciform specimens and notched round specimens subjected to constant amplitude loading
Investigating the PS seismic imaging of faults using seismic modelling and data from the Snøhvit field, Barents Sea
No full textThe Comparison Some Extended Weibull Distribution (Weibull (W), Exponentiated Weibull (EW), Exponentiated Exponential Weibull (EEW)and Additive Weibull (AW)) for the wind Speed Probability Modelling
No full textAccurate wind speed modeling is critical in estimating wind energy potential for harnessing
wind power effectively. One of the bases for assessment of wind energy potential for a specified
region is the probability distribution of wind speed, therefore wind speed data is needed to
produce statistical modeling, especially in determining the best probability distribution. For this
purpose, several modified weibull distributions will be used and tested to determine the best
model to describe wind speed in Pekanbaru. The main goal of this study is to find the best fitting
distribution to the daily wind speed measured over Pekanbaru region for the years 1999-2020
by using the four modified weibull distributions, namely Weibull (W), Exponentiated Weibull
(EW), Additive Weibull (AW) and Exponentiated Exponential Weibull (EEW). The maximum
likelihood method will be used to get the estimated parameter value from the distribution used
in this study. Furthermore, the graphical inspection (density-density plot and cumulative plot)
and numerical criteria (Akaike’s information criterion (AIC), Bayesian Information Criteria
(BIC), - log likelihood (- l) ) were used to determine the best fit model. In most cases, the results
produced by the graphical inspection were similar, and differed from the numerical criteria .
The best fit result was chosen as the distribution with the lowest values of AIC, BIC and - l. In
general, the Exponentiated Exponential Weibull (EEW) distribution has been selected as the
best model
Impulse-driven surface breakdown data : a Weibull statistical analysis
No full textSurface breakdown of oil-immersed solids chosen to insulate high-voltage, pulsed-power systems is a problem that can lead to catastrophic failure. Statistical analysis of the breakdown voltages, or times, associated with such liquid-solid interfaces can reveal useful information to aid system designers in the selection of solid materials. Described in this paper are the results of a Weibull statistical analysis, applied to both breakdown-voltage data and time-to-breakdown data generated in gaps consisting of five different solid polymers immersed in mineral oil. Values of the location parameter γ provide an estimate of the applied voltage below which breakdown will not occur, and under uniform-field conditions, γ varied from 192 kV (480 kV/cm) for polypropylene to zero for ultra-high molecular weight polyethylene. Longer times to breakdown were measured for UHMWPE when compared with the other materials. However, high values of the shape parameter β reported in the present paper suggest greater sensitivity to an increase in applied voltage – that is, the probability of breakdown increases more sharply with increasing applied voltage for UHMWPE compared to the other materials. Analysing peak-applied-voltage data, only PP consistently reflected a low value of β across the different sets of test conditions. In general, longer mean times to breakdown were found for solid materials of εr more closely matched to that of the surrounding mineral oi
A Capacity Supply Model for Virtualized Servers
No full textThis paper deals with determining the capacity supply for virtualized servers. First, a server is modeled as a queue based on a Markov chain. Then, the effect of server virtualization on the capacity supply will be analyzed with the distribution function of the server load.Markov chain, Weibull distribution, server, capacity supply
Applications of the Weibull distribution
No full textA summary or the Weibull distribution and three representative sampling procedures to determine point and confidence interval estimates of the parameters that occur in the functional form of the Weibull distribution are presented. Following this, a model, assuming
the Weibull distribution, is proposed which could have possible applications in analyzing Polaris Missile System Trouble Failure Reports to determine point estimates of the reliability of the Polaris Missile components.
I am indebted to Professor P. W. Zehna tor his continued patience, encouragement, and most capable guidance while acting as faculty advisor. I also wish to thank Professor W.M. Woods tor his valuable assistance as second reader.Approved for public release; distribution is unlimited.Lieutenant, United States Navyhttp://archive.org/details/applicationsofwe109451168
The linearly decreasing stress Weibull (LDSWeibull): a new Weibull-like distribution
No full text© 2019, The Author(s). cc-byMotivated by an engineering pullout test applied to a steel strip embedded in earth, we show how the resulting linearly decreasing force leads naturally to a new distribution, if the force under constant stress is modeled via a three-parameter Weibull. We term this the LDSWeibull distribution, and show that inference on the parameters of the underlying Weibull can be made upon collection of data from such pullout tests. Various classical finite-sample and asymptotic properties of the LDSWeibull are studied, including existence of moments, distribution of extremes, and maximum likelihood based inference under different regimes. The LDSWeibull is shown to have many similarities with the Weibull, but does not suffer from the problem of having an unbounded likelihood function under certain parameter configurations. We demonstrate that the quality of its fit can also be very competitive with that of the Weibull in certain applications
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